The invention relates to a combustor liner v-band louver, which may be manufactured of cast segments and removably fastened to the combustor liner.
Gas turbine engine combustors are relatively thin sheet metal shells surrounded by a plenum containing compressed air from the compressor. Air flows into the combustor through the fuel nozzles to mix with the fuel and through several small openings or louvers in the combustor liner wall which create an air curtain along the inside surface of the combustor liner, provide further air for combusting the fuel and create circulation currents of gas and air flowing within the combustor.
Conventional combustors may include circumferential V-shaped bands machined into inner wall surfaces, that protrude into the combustor from the liner surface or sheet metal double band louver, to generate single or double toroidial fluid flow in the primary combustion zone. In an annular combustor the toroidial flow increases gas residence time in the combustor and thereby improves the fuel/air mixing, engine efficiency and reduces emission levels.
Conventional so-called machined V-band louvers as well double band sheet metal louvers protrude into the hot gas path and are exposed to a harsh environment of rapidly flowing hot gases which tend to oxidize the metal liner material.
A particular disadvantage of conventional machined V-band or standard double band sheet metal louvers circumferential louvers is the development of axial cracks due to the high hoop stresses resulting from temperature differentials. Thermal expansion and contraction stresses exerted on the louver together with the high temperatures expose these protruding components of the combustor wall to durability problems including cracking and oxidation.
Further, V-band lovers or other similar machined louvers are very expensive to manufacture and often require repair during engine overhauls. Conventional combustor liner designs however incorporate the V-band louvers in the unitary machined structure of the combustor liner, and so repair is required to the liner itself.
It is an object of the present invention to provide a more cost effective means of generating the single or double toroidal flow in the primary zone of the combustor liner.
It is a further object of the invention to reduce or eliminate the high hoop stresses in the combustor liner which promote the development of axial cracks in the prior art.
It is a further object of the invention to reduce the cost of manufacture and repair of a combustor liner.
Further objects of the invention will be apparent from review of the disclosure, drawings and description of the invention below.
The invention provides a combustor wall louver for ducting a flow of compressed air through an inlet opening in the combustor wall from a source of compressed air outside the combustor where the louver is a circumferentially extending band member, mounted to an interior surface of the combustor wall and covering the inlet opening with outlet openings fed by a channel in flow communication between each outlet opening and the inlet opening. Preferably, the circumferential band member is made of arcuate segments of cast metal removably mounted to the interior surface of the combustor wall with threaded studs.
As in the prior art, the primary function of the machined V-band/sheet metal double band louver is to generate single or double toroidal flow pattern in the combustor liner to promote fuel combustion efficiency, increase residence time and reduce emissions. However the invention permits reduction in machining required to create the toroidial flow inducing feature in the combustor liner, easing the assembly due to bolted construction and permitting repair or replacement of only the damaged sections through use of separate segments to assemble a circumferential band member about the combustor liner wall.
A benefit of the segmental construction is the reduction of hoop stresses and increasing of the fatigue life of the V-band. Prior art designs induce significant hoop stresses due to the unitary annular structure when exposed to temperature differentials or fluctuations. By creating separate, preferably cast, segments which are assembled together to form the circumferential louver assembly, hoop stresses and axial cracking due to thermal expansion and contraction can be reduced.
In addition, the segmental construction permits a higher degree of assembly and manufacturing tolerance and permits the segments to be manufactured of metals or other materials which have different oxidation or other characteristics and different fatigue strength than the combustor liner to which they are releasably fastened. A segmented cast metal construction is more cost effective to manufacture than conventional designs due to reduced machining, and assembly is simplified by the bolted connection. These features result in lower cost operation since oxidation damaged sections can be replaced individually in a simple bolted connection.
A further advantage of the invention is the diversion of any leakage between the cast V-band segment and the section of the combustor liner wall to which it is releasable attached. Leakage of air through any gap between the cast V-band segment and the combustor liner forms a beneficial film or curtain cooling layer adjacent the liner in the immediate local area.